Surface contact fatigue may contribute and be the dominant cause of power transmission component failure over time. Contact fatigue differs from classic structural fatigue because it may result from a contact or Hertzian stress state. This localized stress state results when curved surfaces are in contact under a normal load. Subsurface plastic strain may build up with increasing cycles until a crack is generated. The crack may then propagate until a pit is formed. Once surface pitting has initiated, the bearing becomes noisy and rough running. If allowed to continue, fracture of the rolling element and failure occurs. Prediction of surface contact fatigue leading to failure may be expensive and time-consuming due to heavy experimentation that may be required.